linux-kernel - [PATCH v2 2/2] mm: fix missing cache flush for all tail pages of THP

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Message-Id: <20220124051752.83281-2-songmuchun@bytedance.com>
Date:   Mon, 24 Jan 2022 13:17:52 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     akpm@...ux-foundation.org, zi.yan@...rutgers.edu,
        kirill.shutemov@...ux.intel.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        duanxiongchun@...edance.com, Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v2 2/2] mm: fix missing cache flush for all tail pages of THP

The D-cache maintenance inside move_to_new_page() only consider one page,
there is still D-cache maintenance issue for tail pages of THP. Fix this
by not using flush_dcache_folio() since it is not backportable.

Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path")
Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
Changes in v2:
 - Using a for loop instead of the folio variant for backportable.

 mm/migrate.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index c9296d63878d..c418e8d92b9c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -933,9 +933,12 @@ static int move_to_new_page(struct page *newpage, struct page *page,
 		if (!PageMappingFlags(page))
 			page->mapping = NULL;
 
-		if (likely(!is_zone_device_page(newpage)))
-			flush_dcache_page(newpage);
+		if (likely(!is_zone_device_page(newpage))) {
+			int i, nr = compound_nr(newpage);
 
+			for (i = 0; i < nr; i++)
+				flush_dcache_page(newpage + i);
+		}
 	}
 out:
 	return rc;
-- 
2.11.0